The present invention relates to a device for continuously manufacturing foam cushions for packaging purposes, said device comprising a supply station and a foam dispensing station, said supply station being provided for continuously supplying to the dispensing station a web of envelope forming material positioned in a face to face relationship so as to form a folded-over edge, said dispensing station comprising a dispensing member provided for supplying a foaming substance into said envelope forming material, said dispensing member having an output oriented towards said edge, said device further comprises transport means provided for transporting said material through said dispensing station according to a predetermined direction, said device also comprises a sealing member provided on the one hand for forming a first and a second seam spaced apart from each other and extending substantially perpendicular to said direction and a third intermittent seam substantially parallel to said direction, said device comprising a cutting member provided for applying a cutting line between said first and second seam.
Such a device is known from EP-A-0.395.438. With the known device the supplied web material is transported in a vertical downwardly oriented direction by the transport means. The first and second seam as well as the cutting line are applied at a bottom part of the device in a horizontal direction perpendicular to the transport direction of the web. The foaming substance is injected into the envelope formed by the web material. The foaming substance is either injected in a vertical or in a horizontal direction.
A drawback of the known device is that when the foaming substance is injected in a vertical direction, it is injected against the second seam which forms the bottom of the cushion. As the second seam has just been applied, care has to be taken that this second seam is not broken by a too heavy injection force. When on the other hand the foaming substance is injected in a horizontal direction, perpendicular to the transport direction, the foaming substance has to be propelled over a suitable distance, which requires a considerable injection power. Irrespective of the direction according to which the foaming substance is injected, gravity will always cause the foaming substance to fall on the bottom of the cushion which is formed. This signifies that foaming substances, generally in liquid form, fall over the already applied foaming substances which are reacting in order to form foam. The thus created mixture of reacting foaming substances with liquid substances considerably disturbs the reacting process and the yield of the latter. Moreover this mixture also leads to an irregular cell structure of the foam caused by the foaming under chaotic conditions in a restricted volume.
The object of the invention is to realise a device for continuously manufacturing foam cushions enabling an improved foaming reaction leading to a better foam quality and with a considerably lower risk of damaging the second seam.
For this purpose a device according to the present invention is characterised in that said transport means are provided for transporting said web material in a substantially horizontal direction and comprises a guiding and clamping unit provided for guiding said edge along said direction and clamping said material over a predetermined stroke extending from said edge in a further direction substantially perpendicular to said direction. Because the web material is transported in a horizontal direction and the dispensing member""s output is oriented towards the edge, the foaming material is not dispensed against the seams which extend perpendicular to the edge. The gravity will cause the foaming substance to fall on the edge and not on the seam. The risk of damaging the edge is thus substantially reduced. Moreover the guiding and clamping unit guide and support the edge so that the risk of damaging the edge is to be neglected. Because the web material moves in horizontal direction, the supplied foaming substances reaching the edge also move in the same horizontal direction. In such a manner the newly supplied liquid foaming substances do substantially less mix with the reacting foaming substances which move away from the dispensing member. So the liquid material substantially less disturbs the foaming reaction of the substances and a better foam quality is obtained.
A first preferred embodiment of a device according to the invention is characterised in that said guiding and clamping unit comprise a first and a second beam applied face to face, at least one of them being resiliently mounted. The edge can in such a manner be reliably guided by the two beams in between which it is clamped. The resilient mounting of at least one beam facilitates the supply of the web material.
A second preferred embodiment of a device according to the invention is characterised in that said transport means are further provided for applying a double fold at said folded-over edge. The double fold strengthens the edge and reduces the risks of damaging the edge. It moreover enables to improve the guiding of the edge as it makes the edge thicker.
Preferably said dispensing member is mounted on a movable arm provided for being moved between a first and second position whereby said dispensing member is placed inside, respectively outside a volume delimited by the envelope forming material. In such a manner the dispensing member can be removed from the volume formed by the web material.
Preferably a cleaning unit is applied at said second position, said cleaning unit being provided for cleaning said dispensing member. The dispensing member can thus be cleaned from remaining foaming substances, which could obstruct the output of the dispensing member.
A third preferred embodiment of a device according to the invention is characterised in that said transport means comprise a first and a second roller set, the rollers of each set being mounted at a predetermined distance from each other and extending substantially perpendicular to said direction at opposite sides of each web, said predetermined distance being at least 5 mm. In such a manner a cushion of predetermined thickness can be formed.
A fourth preferred embodiment of a device according to the invention is characterised in that said transport means comprise a first and second toothed roller mounted in an engaging manner at opposite sides of said web. The toothed roller enables a good mixing of the foaming substances when the mixing is not performed by the dispensing